Field coils for stators of dynamo-electric machines are generally placed on radially inwardly extending teeth of the stator as wire windings. In stators used for motors, the motor performance may be affected by the size and geometry of the motor and by the “active materials” forming the motor. In a brushless DC motor, for example, the active materials may comprise steel, magnets and copper forming the motor windings. For a given motor size, comprising a fixed amount of steel and magnet, providing additional windings (copper) located in the stator slots provides an increased amount of torque. Alternatively, if the field coils are formed with additional windings, it may be possible to reduce the axial length of the stator while maintaining the same performance that was achieved with a longer stator and lower number of windings. Generally, the slot geometry for stators is fixed such that the amount of the slot area that is filled with copper, i.e., the slot fill, is dependent on the efficiency with which the windings are positioned adjacent to each other within the slots.
Various factors affect the ability to efficiently position windings within the stator slots including interference from windings already positioned in a slot as additional wire is located in the slot. Thus, winding operations commonly involve a forming operation in which windings are periodically pushed or formed into closer engagement with each other to provide additional slot clearance for receiving further windings. In addition, in series wound stators, winding wire that extends across two or more slots defined between adjacent teeth at an end of the stator, i.e., cross-overs, may form a partial barrier covering a radial portion of the slots and limiting the amount of wire that may be added to the slots.